1. Field of the Invention
This invention relates to improving the heat stability of acrylamide functional polyorganosiloxanes.
2. Background Information
Polyorganosiloxane are known to have valuable properties for protecting surfaces from environmental attack such as from weather, chemical, cold, and heat. However, each of these have limitations and improvement is still sought, so that, the materials can be used in harsher environments than was previously possible. Polyorganosiloxanes provide electrical insulating properties which make them useful in the electronics industry for coatings, encapsulants, and potting materials. For example, a printed circuit board may find utility in an engine of an automobile or other vehicle, but the temperatures may be too high for prolonged exposure and the polyorganosiloxane materials may not maintain their functional properties adequately. However, if one can increase the serviceable temperature of the polyorganosiloxane material, maybe a coated printed circuit board might be useful for applications where it will be exposed to high temperatures. The polyorganosiloxane should maintain sufficient physical integrity to protect the device it is covering and also it should not release degradation products which may harm delicate instrumentation.
The use of polyorganosiloxane materials which will cure by exposure to ultraviolet radiation provide the advantages of fast curing, low amounts of volatiles given off during curing, readily applicable to automation, cure at low temperatures and reduced energy costs. These are some of the reasons for today's industry wanting to use both polyorganosiloxanes and the ultraviolet radiation curing combination. However, many of the polyorganosiloxane compositions which may be cured by exposure to ultraviolet radiation have relatively low tolerance to prolonged exposure to high temperatures without degrading or loosing their physical properties. To make them more desirable for applications protecting surfaces from environments during and after exposure to high temperatures, the heat or thermal stability needs to be improved. Therefore, a search was conducted to find a means for increasing the serviceable temperature of ultraviolet radiation curable polyorganosiloxane compositions. The means should overcome the effects of exposure to high temperature, such as loss of mechanical strength and toughness, embrittlement and cracking, and reduction in electrical properties.